[How-To] Provide a password to su from the command line

How to provide a password to SU from the command line or from a script

For security reasons, /bin/su does not accept a password from the command line:

user@host$ echo pass | su -c id
su: must be run from a terminal

When you can execute commands on a system but you don't have an interactive shell (these things happen), then you can't use su this way.

But using socat, you can simulate a tty for any program and provide the input from STDIN, a socket, a file, whatever...

Here is how you would run it:

user@host$ (sleep 1; echo SuperSecr3t) | socat - EXEC:'su -c id',pty,ctty,setsid
Password: ### No input here, just wait 1sec
uid=0(root) gid=0(root) groups=0(root)

Taking this further, now imagine that you have a non-interactive shell access as a standard user (user1). On this system, there is another user (user2) who can run commands as root using sudo, but user1 can't. You happen to know the password to the user2 account. What you want to do is switch to user2 via su, then run a command as root using sudo from the user2 account.

Here is how to proceed:

user1@host$ echo -e '#!/bin/sh\necho User2SuperPasswd | sudo -S id' > runasroot.sh
user1@host$ chmod +x runasroot.sh
user1@host$ (sleep 1; echo User2SuperPasswd) | socat - EXEC:'su user2 -c ./runasroot.sh',pty,ctty,setsid
Password: ### No input here, just wait 1 sec
[sudo] password for user2: uid=0(root) gid=0(root) groups=0(root)

How-To: Rdesktop over (HTTP) Proxy

How to connect to a remote desktop host via an HTTP Proxy

In this example we will use, once again, socat. Here is how to connect to a Terminal Server which can be reach only behind an HTTP Proxy.

First, make sure that your $http_proxy environment variable is set properly.

Add the following function to your ~/.bashrc:

function rdesktop_proxy () {
 
 if [ $# -lt 1 ]; then
  echo "usage: $0 <hostname/ip>"
  return
 fi

 HOST=$1
 PROXY_HOST=$(echo $http_proxy | sed 's,http:,,;s,/,,g' | cut -d: -f1)
 PROXY_PORT=$(echo $http_proxy | sed 's,http:,,;s,/,,g' | cut -d: -f2)

 socat TCP4-LISTEN:51515,bind=127.0.0.1,reuseaddr PROXY:$PROXY_HOST:$HOST:3389,proxyport=$PROXY_PORT &

 /usr/local/bin/xfreerdp +clipboard +home-drive "/t:$1" /v:127.0.0.1:51515 "${@:2}"
}

Then re-source your shell:

source ~/.bashrc

And you can just type:

rdesktop_proxy my.rdpdomain.com /u:John

The example above use the xfreerdp client, but you can adjust it to use your favourite RDP client, you get the idea.